This invention relates to the design of electrochemical cells. It has particular application in those cells that employ molten electrolytic salt and operate at high temperatures. Other conventional cells employing aqueous electrolyte and more moderate temperatures might also beneficially include the present cell design.
A substantial amount of work has been done in the development of high-temperature electrochemical cells which exhibit high specific energy. Much of this development has involved cells including alkali metals and their alloys as negative electrodes and chalcogens or metal chalcogenides as positive electrode materials. Such cells employ molten salt electrolyte and consequently operate at elevated temperatures. Special ceramic materials are required as separators and other sealing components within these high-temperature corrosive environments.
Molten salts of the alkali metal and alkaline earth metal halides are often selected as electrolyte for these type cells. Such salts are quite dense, having specific gravities in the range of 3 to 5 such that, if used in large quantities, the salts will significantly add to the cell weight.
Many of the corrosive resistant and high-temperature ceramic materials such as yttria, boron nitride, silicon nitride, aluminum nitride, calcium zirconate and magnesium oxide are difficult and expensive to fabricate into strong porous layers suitable for use as interelectrode separators. Where more frangible forms such as foams and felts are employed, these materials tend to break at corners and ends, introducing the risk of electrical shorting.
One potential field of use for these new electrochemical cells is that of electrical vehicle propulsion. In such applications, the energy storage capability per unit weight (specific energy) become of particular importance. These considerations and other problems associated with past electrochemical cell developments are illustrated in the following prior art.